1. Field of the Invention
The present invention relates to apparatus for preventing premature turn-on of gas after seismic activity. More particularly, this invention pertains to a seismically-activated gas shut-off valve that includes a reset safety lock.
2. Description of the Prior Art
Many structures, both residential and otherwise, are located in areas subject to substantial earthquake activity. The vast majority of such structures include a natural or liquid petroleum gas supply system to run appliances for needs as basic and diverse as cooking and hygiene.
The usual arrangement for supplying gas to a structure from a remote source of natural gas or liquid petroleum gas includes a pressure regulator within a gas main. The pressure regulator serves to modify the gas pressure from its supply or storage level (about 160 p.s.i. for liquid petroleum sources of butane and propane) to a reduced level suitable for use by domestic appliances (about 0.5 p.s.i.). The low pressure is run through a gas meter whose output is, in turn, coupled to a service line for supplying the various appliances within the dwelling.
Shutting off the gas supply to a structure subjected to significant seismic forces is essential to prevent leakage from broken lines. A useful addition to the basic gas supply system described above in areas subject to earthquake-induced lateral acceleration and deceleration forces is a valve within the service pipe whose closure is responsive to such lateral forces. Examples of such valves are disclosed in U.S. Pat. No. 3,747,616 of Hershall E. Lloyd entitled "Earthquake Sensitive Shut-Off Valve" and U.S. Pat. No. 4,889,150 of Hershall E. Lloyd et al. entitled "Pressure Control For Earthquake Sensitive Shut-Off Valve". Each teaches a valve housing that accommodates substantially-vertical internal gas flow channel. A ball valve of a heavy metal fabrication within the valve housing is movable from a first stable position seated upon a saddle de-centered from the vertical flow channel (valve "open") to a second stable position, a valve seat that lies within the flow channel (valve "closed"). The internal structures of the valves are arranged so that the ball valve will tumble from the elevated saddle to the valve seat, causing the flow of gas to be interrupted, in response to earthquake forces.
Once the flow of gas has been interrupted and seismic activity ended, careful inspection must be made of vulnerable structures, such as gas lines, to ascertain their integrity. Leaks create numerous problems after an earthquake as a result of the volatility and toxicity of both natural and petroleum gases. U.S. Pat. No. 4,889,150 teaches a useful arrangement that permits reopening of the gas flow channel in a sealed valve after the valve has been actuated to its closed position. This is accomplished by a means of a horizontally-disposed push pin that is located within a cage at a side of the valve housing opposite the aforesaid saddle. The push pin or piston is fixed to a handle and the unit is slidable within the cage. An aperture in the side of the valve body admits the push pin for contacting the ball valve at such a level that it exerts a horizontal repositioning force, lifting the ball valve from the valve seat onto the elevated saddle. The resetting arrangement is spring-loaded within the cage for automatic retraction when the valve is in its open position.
Ideally, a careful inspection is made of vulnerable structures subsequent to a seismic event. Unfortunately, this does not always take place due to the vulnerability of the valve to unintentional resetting scenarios. The valve is usually installed at a level that is easily-accessible and this can present an irresistible temptation to reset after a period of time has passed without a home supply of gas. Restarting the flow of gas without proper inspection can produce disasters. The relatively low level of installation also subjects the valve to inadvertent resetting by pets and children.